HOUSTON — The Washington Nationals have fired Manny Acta after two and a half seasons and replaced him with bench coach Jim Riggleman.

Acta confirmed to The Washington Times in an e-mail early Monday morning he had been fired after two and a half years as the Nationals’ manager. The Nationals lost 5-0 to the Houston Astros on Sunday, dropping their record to a major league-worst 25-61. The team finished 59-102 in 2008, a mark that also was the worst in baseball.

The 40-year-old’s tenure ends with a 158-252 record. His .385 winning percentage is the 10th-worst in major-league history.

“I thank the Nationals for giving me this opportunity and I’m sorry that things didn’t work out as expected,” Acta told ESPNDeportes.com, which first reported the news. “It’s normal for the manager to pay the price when the team is not doing well.”

Acta, the youngest manager in the major leagues when he was hired, was given a two-year contract with a pair of one-year options and touted as a major piece in the Nationals’ rebuilding project. The team picked up his 2009 option at the end of the 2007 season, but did not give Acta the same show of faith after last season and let go every member of his coaching staff except pitching coach Randy St. Claire. Then, the team fired St. Claire in early June.

Riggleman, who was hired as bench coach last winter, will be introduced today as manager, according to a club source. A news conference is tentatively scheduled for 11 a.m. at Nationals Park.

Riggleman, 56, has managed parts of nine seasons with three previous major league clubs and owns an overall 522-652 record. He went 112-179 with the Padres from 1992-94, 374-491 with the Cubs from 1995-99 (winning the NL wild card in 1998) and 36-54 as the Mariners’ interim manager last season.

Acta spent two years as the New York Mets’ third-base coach before the Nationals hired him to replace Frank Robinson in 2006. He leaves as the longest-tenured manager in Nationals history, still popular with some fans because of his upbeat personality but criticized by others for not taking a tougher tack with his floundering team.